This project is directed toward examining the understudied question, the role of the choriocapillaris in early age-related macular degeneration (AMD). Preliminary data described in the proposal suggest that choriocapillary endothelial cells are a target for complement-mediated cell lysis in AMD. The loss of these cells due to injury, and/or the change in endothelial cell phenotype as a consequence of injury, may be a crucial step in the pathogenesis of this blinding disorder. The proposed studies will address these issues. The applicant proposes that events associated with choriocapillaris endothelial cell injury are likely to lead to lack of perfusion, endothelial cell activation, inflammation, aberrant synthesis or turnover of the extracellular matrix, and/or neovascularization, and therefore may play a significant role in the pathogenesis of AMD. The first specific aim of this project is to examine the association of complement complexes with the choriocapillaris in aging and in early AMD in a large series of donor eyes, and to correlate this association with the morphometric characteristics of the choriocapillaris of the same eyes. The second specific aim is designed to assess endothelial cell activation in association with AMD, which is one response of endothelial cells to complement-mediated injury and inflammation. Quantitative molecular analyses on the isolated choriocapillaris and immunohistochemical studies on human donor eyes will be performed to examine the question of endothelial cell activation in AMD. The third specific aim is to examine the behavior of choriocapillaris cells in vitro, particularly in response to complement mediated injury. Organ cultures of the choroid will be treated with conditions that promote complement complex formation, followed by immunohistochemical and molecular analyses. Endothelial cell cultures will be prepared from human donor eyes, with the long-term goal of assessing their response to complement-mediated injury and other types of injury. The development of these cultures will represent an essential resource for future studies by the applicant in this field. These experiments are expected to provide novel insights into the potential role of the choriocapillaris in the pathobiology of AMD.